The Solar Wind Environment in Time

We use magnetograms of eight solar analogs of ages 30 Myr-3.6 Gyr obtained from Zeeman Doppler Imaging and taken from the literature, together with two solar magnetograms, to drive magnetohydrodynamical wind simulations and construct an evolutionary scenario of the solar wind environment and its angular momentum loss rate. With observed magnetograms of the radial field strength as the only variant in the wind model, we find that a power-law model fitted to the derived angular momentum loss rate against time, t, results in a spin-down relation Omega alpha t(-0.51), for angular speed Omega, which is remarkably consistent with the well-established Skumanich law Omega alpha t(-0.5). We use the model wind conditions to estimate the magnetospheric standoff distances for an Earth-like test planet situated at 1 au for each of the stellar cases, and to obtain trends of minimum and maximum wind ram pressure and average ram pressure in the solar system through time. The wind ram pressure declines with time as (P-ram) over bar alpha t(2/3), amounting to a factor of 50 or so over the present lifetime of the solar system.